backbone.js

//     Backbone.js 0.3.2
//     (c) 2010 Jeremy Ashkenas, DocumentCloud Inc.
//     Backbone may be freely distributed under the MIT license.
//     For all details and documentation:
//     http://documentcloud.github.com/backbone

(function(){

  // Initial Setup
  // -------------

  // The top-level namespace. All public Backbone classes and modules will
  // be attached to this. Exported for both CommonJS and the browser.
  var Backbone;
  if (typeof exports !== 'undefined') {
    Backbone = exports;
  } else {
    Backbone = this.Backbone = {};
  }

  // Current version of the library. Keep in sync with `package.json`.
  Backbone.VERSION = '0.3.2';

  // Require Underscore, if we're on the server, and it's not already present.
  var _ = this._;
  if (!_ && (typeof require !== 'undefined')) _ = require("underscore")._;

  // For Backbone's purposes, jQuery owns the `$` variable.
  var $ = this.jQuery;

  // Turn on `emulateHTTP` to use support legacy HTTP servers. Setting this option will
  // fake `"PUT"` and `"DELETE"` requests via the `_method` parameter and set a
  // `X-Http-Method-Override` header.
  Backbone.emulateHTTP = false;

  // Turn on `emulateJSON` to support legacy servers that can't deal with direct
  // `application/json` requests ... will encode the body as
  // `application/x-www-form-urlencoded` instead and will send the model in a
  // form param named `model`.
  Backbone.emulateJSON = false;

  // Backbone.Events
  // -----------------

  // A module that can be mixed in to *any object* in order to provide it with
  // custom events. You may `bind` or `unbind` a callback function to an event;
  // `trigger`-ing an event fires all callbacks in succession.
  //
  //     var object = {};
  //     _.extend(object, Backbone.Events);
  //     object.bind('expand', function(){ alert('expanded'); });
  //     object.trigger('expand');
  //
  Backbone.Events = {

    // Bind an event, specified by a string name, `ev`, to a `callback` function.
    // Passing `"all"` will bind the callback to all events fired.
    bind : function(ev, callback) {
      var calls = this._callbacks || (this._callbacks = {});
      var list  = this._callbacks[ev] || (this._callbacks[ev] = []);
      list.push(callback);
      return this;
    },

    // Remove one or many callbacks. If `callback` is null, removes all
    // callbacks for the event. If `ev` is null, removes all bound callbacks
    // for all events.
    unbind : function(ev, callback) {
      var calls;
      if (!ev) {
        this._callbacks = {};
      } else if (calls = this._callbacks) {
        if (!callback) {
          calls[ev] = [];
        } else {
          var list = calls[ev];
          if (!list) return this;
          for (var i = 0, l = list.length; i < l; i++) {
            if (callback === list[i]) {
              list.splice(i, 1);
              break;
            }
          }
        }
      }
      return this;
    },

    // Trigger an event, firing all bound callbacks. Callbacks are passed the
    // same arguments as `trigger` is, apart from the event name.
    // Listening for `"all"` passes the true event name as the first argument.
    trigger : function(ev) {
      var list, calls, i, l;
      if (!(calls = this._callbacks)) return this;
      if (list = calls[ev]) {
        for (i = 0, l = list.length; i < l; i++) {
          list[i].apply(this, Array.prototype.slice.call(arguments, 1));
        }
      }
      if (list = calls['all']) {
        for (i = 0, l = list.length; i < l; i++) {
          list[i].apply(this, arguments);
        }
      }
      return this;
    }

  };

  // Backbone.Model
  // --------------

  // Create a new model, with defined attributes. A client id (`cid`)
  // is automatically generated and assigned for you.
  Backbone.Model = function(attributes, options) {
    attributes || (attributes = {});
    if (this.defaults) attributes = _.extend({}, this.defaults, attributes);
    this.attributes = {};
    this.cid = _.uniqueId('c');
    this.set(attributes, {silent : true});
    this._previousAttributes = _.clone(this.attributes);
    if (options && options.collection) this.collection = options.collection;
    this.initialize(attributes, options);
  };

  // Attach all inheritable methods to the Model prototype.
  _.extend(Backbone.Model.prototype, Backbone.Events, {

    // A snapshot of the model's previous attributes, taken immediately
    // after the last `"change"` event was fired.
    _previousAttributes : null,

    // Has the item been changed since the last `"change"` event?
    _changed : false,

    // Initialize is an empty function by default. Override it with your own
    // initialization logic.
    initialize : function(){},

    // Return a copy of the model's `attributes` object.
    toJSON : function() {
      return _.clone(this.attributes);
    },

    // Get the value of an attribute.
    get : function(attr) {
      return this.attributes[attr];
    },

    // Set a hash of model attributes on the object, firing `"change"` unless you
    // choose to silence it.
    set : function(attrs, options) {

      // Extract attributes and options.
      options || (options = {});
      if (!attrs) return this;
      if (attrs.attributes) attrs = attrs.attributes;
      var now = this.attributes;

      // Run validation.
      if (!options.silent && this.validate && !this._performValidation(attrs, options)) return false;

      // Check for changes of `id`.
      if ('id' in attrs) this.id = attrs.id;

      // Update attributes.
      for (var attr in attrs) {
        var val = attrs[attr];
        if (!_.isEqual(now[attr], val)) {
          now[attr] = val;
          if (!options.silent) {
            this._changed = true;
            this.trigger('change:' + attr, this, val);
          }
        }
      }

      // Fire the `"change"` event, if the model has been changed.
      if (!options.silent && this._changed) this.change();
      return this;
    },

    // Remove an attribute from the model, firing `"change"` unless you choose
    // to silence it.
    unset : function(attr, options) {
      options || (options = {});
      var value = this.attributes[attr];

      // Run validation.
      var validObj = {};
      validObj[attr] = void 0;
      if (!options.silent && this.validate && !this._performValidation(validObj, options)) return false;

      // Remove the attribute.
      delete this.attributes[attr];
      if (!options.silent) {
        this._changed = true;
        this.trigger('change:' + attr, this);
        this.change();
      }
      return this;
    },

    // Clear all attributes on the model, firing `"change"` unless you choose
    // to silence it.
    clear : function(options) {
      options || (options = {});
      var old = this.attributes;

      // Run validation.
      var validObj = {};
      for (attr in old) validObj[attr] = void 0;
      if (!options.silent && this.validate && !this._performValidation(validObj, options)) return false;

      this.attributes = {};
      if (!options.silent) {
        this._changed = true;
        for (attr in old) {
          this.trigger('change:' + attr, this);
        }
        this.change();
      }
      return this;
    },

    // Fetch the model from the server. If the server's representation of the
    // model differs from its current attributes, they will be overriden,
    // triggering a `"change"` event.
    fetch : function(options) {
      options || (options = {});
      var model = this;
      var success = function(resp) {
        if (!model.set(model.parse(resp), options)) return false;
        if (options.success) options.success(model, resp);
      };
      var error = options.error && _.bind(options.error, null, model);
      (this.sync || Backbone.sync)('read', this, success, error);
      return this;
    },

    // Set a hash of model attributes, and sync the model to the server.
    // If the server returns an attributes hash that differs, the model's
    // state will be `set` again.
    save : function(attrs, options) {
      options || (options = {});
      if (attrs && !this.set(attrs, options)) return false;
      var model = this;
      var success = function(resp) {
        if (!model.set(model.parse(resp), options)) return false;
        if (options.success) options.success(model, resp);
      };
      var error = options.error && _.bind(options.error, null, model);
      var method = this.isNew() ? 'create' : 'update';
      (this.sync || Backbone.sync)(method, this, success, error);
      return this;
    },

    // Destroy this model on the server. Upon success, the model is removed
    // from its collection, if it has one.
    destroy : function(options) {
      options || (options = {});
      var model = this;
      var success = function(resp) {
        if (model.collection) model.collection.remove(model);
        if (options.success) options.success(model, resp);
      };
      var error = options.error && _.bind(options.error, null, model);
      (this.sync || Backbone.sync)('delete', this, success, error);
      return this;
    },

    // Default URL for the model's representation on the server -- if you're
    // using Backbone's restful methods, override this to change the endpoint
    // that will be called.
    url : function() {
      var base = getUrl(this.collection);
      if (this.isNew()) return base;
      return base + (base.charAt(base.length - 1) == '/' ? '' : '/') + this.id;
    },

    // **parse** converts a response into the hash of attributes to be `set` on
    // the model. The default implementation is just to pass the response along.
    parse : function(resp) {
      return resp;
    },

    // Create a new model with identical attributes to this one.
    clone : function() {
      return new this.constructor(this);
    },

    // A model is new if it has never been saved to the server, and has a negative
    // ID.
    isNew : function() {
      return !this.id;
    },

    // Call this method to manually fire a `change` event for this model.
    // Calling this will cause all objects observing the model to update.
    change : function() {
      this.trigger('change', this);
      this._previousAttributes = _.clone(this.attributes);
      this._changed = false;
    },

    // Determine if the model has changed since the last `"change"` event.
    // If you specify an attribute name, determine if that attribute has changed.
    hasChanged : function(attr) {
      if (attr) return this._previousAttributes[attr] != this.attributes[attr];
      return this._changed;
    },

    // Return an object containing all the attributes that have changed, or false
    // if there are no changed attributes. Useful for determining what parts of a
    // view need to be updated and/or what attributes need to be persisted to
    // the server.
    changedAttributes : function(now) {
      now || (now = this.attributes);
      var old = this._previousAttributes;
      var changed = false;
      for (var attr in now) {
        if (!_.isEqual(old[attr], now[attr])) {
          changed = changed || {};
          changed[attr] = now[attr];
        }
      }
      return changed;
    },

    // Get the previous value of an attribute, recorded at the time the last
    // `"change"` event was fired.
    previous : function(attr) {
      if (!attr || !this._previousAttributes) return null;
      return this._previousAttributes[attr];
    },

    // Get all of the attributes of the model at the time of the previous
    // `"change"` event.
    previousAttributes : function() {
      return _.clone(this._previousAttributes);
    },

    // Run validation against a set of incoming attributes, returning `true`
    // if all is well. If a specific `error` callback has been passed,
    // call that instead of firing the general `"error"` event.
    _performValidation : function(attrs, options) {
      var error = this.validate(attrs);
      if (error) {
        if (options.error) {
          options.error(this, error);
        } else {
          this.trigger('error', this, error);
        }
        return false;
      }
      return true;
    }

  });

  // Backbone.Collection
  // -------------------

  // Provides a standard collection class for our sets of models, ordered
  // or unordered. If a `comparator` is specified, the Collection will maintain
  // its models in sort order, as they're added and removed.
  Backbone.Collection = function(models, options) {
    options || (options = {});
    if (options.comparator) {
      this.comparator = options.comparator;
      delete options.comparator;
    }
    this._boundOnModelEvent = _.bind(this._onModelEvent, this);
    this._reset();
    if (models) this.refresh(models, {silent: true});
    this.initialize(models, options);
  };

  // Define the Collection's inheritable methods.
  _.extend(Backbone.Collection.prototype, Backbone.Events, {

    // The default model for a collection is just a **Backbone.Model**.
    // This should be overridden in most cases.
    model : Backbone.Model,

    // Initialize is an empty function by default. Override it with your own
    // initialization logic.
    initialize : function(){},

    // The JSON representation of a Collection is an array of the
    // models' attributes.
    toJSON : function() {
      return this.map(function(model){ return model.toJSON(); });
    },

    // Add a model, or list of models to the set. Pass **silent** to avoid
    // firing the `added` event for every new model.
    add : function(models, options) {
      if (_.isArray(models)) {
        for (var i = 0, l = models.length; i < l; i++) {
          this._add(models[i], options);
        }
      } else {
        this._add(models, options);
      }
      return this;
    },

    // Remove a model, or a list of models from the set. Pass silent to avoid
    // firing the `removed` event for every model removed.
    remove : function(models, options) {
      if (_.isArray(models)) {
        for (var i = 0, l = models.length; i < l; i++) {
          this._remove(models[i], options);
        }
      } else {
        this._remove(models, options);
      }
      return this;
    },

    // Get a model from the set by id.
    get : function(id) {
      if (id == null) return null;
      return this._byId[id.id != null ? id.id : id];
    },

    // Get a model from the set by client id.
    getByCid : function(cid) {
      return cid && this._byCid[cid.cid || cid];
    },

    // Get the model at the given index.
    at: function(index) {
      return this.models[index];
    },

    // Force the collection to re-sort itself. You don't need to call this under normal
    // circumstances, as the set will maintain sort order as each item is added.
    sort : function(options) {
      options || (options = {});
      if (!this.comparator) throw new Error('Cannot sort a set without a comparator');
      this.models = this.sortBy(this.comparator);
      if (!options.silent) this.trigger('refresh', this);
      return this;
    },

    // Pluck an attribute from each model in the collection.
    pluck : function(attr) {
      return _.map(this.models, function(model){ return model.get(attr); });
    },

    // When you have more items than you want to add or remove individually,
    // you can refresh the entire set with a new list of models, without firing
    // any `added` or `removed` events. Fires `refresh` when finished.
    refresh : function(models, options) {
      models  || (models = []);
      options || (options = {});
      this._reset();
      this.add(models, {silent: true});
      if (!options.silent) this.trigger('refresh', this);
      return this;
    },

    // Fetch the default set of models for this collection, refreshing the
    // collection when they arrive.
    fetch : function(options) {
      options || (options = {});
      var collection = this;
      var success = function(resp) {
        collection.refresh(collection.parse(resp));
        if (options.success) options.success(collection, resp);
      };
      var error = options.error && _.bind(options.error, null, collection);
      (this.sync || Backbone.sync)('read', this, success, error);
      return this;
    },

    // Create a new instance of a model in this collection. After the model
    // has been created on the server, it will be added to the collection.
    create : function(model, options) {
      var coll = this;
      options || (options = {});
      if (!(model instanceof Backbone.Model)) {
        model = new this.model(model, {collection: coll});
      } else {
        model.collection = coll;
      }
      var success = function(nextModel, resp) {
        coll.add(nextModel);
        if (options.success) options.success(nextModel, resp);
      };
      return model.save(null, {success : success, error : options.error});
    },

    // **parse** converts a response into a list of models to be added to the
    // collection. The default implementation is just to pass it through.
    parse : function(resp) {
      return resp;
    },

    // Proxy to _'s chain. Can't be proxied the same way the rest of the
    // underscore methods are proxied because it relies on the underscore
    // constructor.
    chain: function () {
      return _(this.models).chain();
    },

    // Reset all internal state. Called when the collection is refreshed.
    _reset : function(options) {
      this.length = 0;
      this.models = [];
      this._byId  = {};
      this._byCid = {};
    },

    // Internal implementation of adding a single model to the set, updating
    // hash indexes for `id` and `cid` lookups.
    _add : function(model, options) {
      options || (options = {});
      if (!(model instanceof Backbone.Model)) {
        model = new this.model(model, {collection: this});
      }
      var already = this.getByCid(model);
      if (already) throw new Error(["Can't add the same model to a set twice", already.id]);
      this._byId[model.id] = model;
      this._byCid[model.cid] = model;
      model.collection = this;
      var index = this.comparator ? this.sortedIndex(model, this.comparator) : this.length;
      this.models.splice(index, 0, model);
      model.bind('all', this._boundOnModelEvent);
      this.length++;
      if (!options.silent) model.trigger('add', model, this);
      return model;
    },

    // Internal implementation of removing a single model from the set, updating
    // hash indexes for `id` and `cid` lookups.
    _remove : function(model, options) {
      options || (options = {});
      model = this.getByCid(model) || this.get(model);
      if (!model) return null;
      delete this._byId[model.id];
      delete this._byCid[model.cid];
      delete model.collection;
      this.models.splice(this.indexOf(model), 1);
      this.length--;
      if (!options.silent) model.trigger('remove', model, this);
      model.unbind('all', this._boundOnModelEvent);
      return model;
    },

    // Internal method called every time a model in the set fires an event.
    // Sets need to update their indexes when models change ids. All other
    // events simply proxy through.
    _onModelEvent : function(ev, model) {
      if (ev === 'change:id') {
        delete this._byId[model.previous('id')];
        this._byId[model.id] = model;
      }
      this.trigger.apply(this, arguments);
    }

  });

  // Underscore methods that we want to implement on the Collection.
  var methods = ['forEach', 'each', 'map', 'reduce', 'reduceRight', 'find', 'detect',
    'filter', 'select', 'reject', 'every', 'all', 'some', 'any', 'include',
    'invoke', 'max', 'min', 'sortBy', 'sortedIndex', 'toArray', 'size',
    'first', 'rest', 'last', 'without', 'indexOf', 'lastIndexOf', 'isEmpty'];

  // Mix in each Underscore method as a proxy to `Collection#models`.
  _.each(methods, function(method) {
    Backbone.Collection.prototype[method] = function() {
      return _[method].apply(_, [this.models].concat(_.toArray(arguments)));
    };
  });

  // Backbone.Controller
  // -------------------

  // Controllers map faux-URLs to actions, and fire events when routes are
  // matched. Creating a new one sets its `routes` hash, if not set statically.
  Backbone.Controller = function(options) {
    options || (options = {});
    if (options.routes) this.routes = options.routes;
    this._bindRoutes();
    this.initialize(options);
  };

  // Cached regular expressions for matching named param parts and splatted
  // parts of route strings.
  var namedParam = /:([\w\d]+)/g;
  var splatParam = /\*([\w\d]+)/g;

  // Set up all inheritable **Backbone.Controller** properties and methods.
  _.extend(Backbone.Controller.prototype, Backbone.Events, {

    // Initialize is an empty function by default. Override it with your own
    // initialization logic.
    initialize : function(){},

    // Manually bind a single named route to a callback. For example:
    //
    //     this.route('search/:query/p:num', 'search', function(query, num) {
    //       ...
    //     });
    //
    route : function(route, name, callback) {
      Backbone.history || (Backbone.history = new Backbone.History);
      if (!_.isRegExp(route)) route = this._routeToRegExp(route);
      Backbone.history.route(route, _.bind(function(fragment) {
        var args = this._extractParameters(route, fragment);
        callback.apply(this, args);
        this.trigger.apply(this, ['route:' + name].concat(args));
      }, this));
    },

    // Simple proxy to `Backbone.history` to save a fragment into the history,
    // without triggering routes.
    saveLocation : function(fragment) {
      Backbone.history.saveLocation(fragment);
    },

    // Bind all defined routes to `Backbone.history`.
    _bindRoutes : function() {
      if (!this.routes) return;
      for (var route in this.routes) {
        var name = this.routes[route];
        this.route(route, name, this[name]);
      }
    },

    // Convert a route string into a regular expression, suitable for matching
    // against the current location fragment.
    _routeToRegExp : function(route) {
      route = route.replace(namedParam, "([^\/]*)").replace(splatParam, "(.*?)");
      return new RegExp('^' + route + '$');
    },

    // Given a route, and a URL fragment that it matches, return the array of
    // extracted parameters.
    _extractParameters : function(route, fragment) {
      return route.exec(fragment).slice(1);
    }

  });

  // Backbone.History
  // ----------------

  // Handles cross-browser history management, based on URL hashes. If the
  // browser does not support `onhashchange`, falls back to polling.
  Backbone.History = function() {
    this.handlers = [];
    this.fragment = this.getFragment();
    _.bindAll(this, 'checkUrl');
  };

  // Cached regex for cleaning hashes.
  var hashStrip = /^#*/;

  // Set up all inheritable **Backbone.History** properties and methods.
  _.extend(Backbone.History.prototype, {

    // The default interval to poll for hash changes, if necessary, is
    // twenty times a second.
    interval: 50,

    // Get the cross-browser normalized URL fragment.
    getFragment : function(loc) {
      return (loc || window.location).hash.replace(hashStrip, '');
    },

    // Start the hash change handling, returning `true` if the current URL matches
    // an existing route, and `false` otherwise.
    start : function() {
      var docMode = document.documentMode;
      var oldIE = ($.browser.msie && (!docMode || docMode <= 7));
      if (oldIE) {
        this.iframe = $('<iframe src="javascript:0" tabindex="-1" />').hide().appendTo('body')[0].contentWindow;
      }
      if ('onhashchange' in window && !oldIE) {
        $(window).bind('hashchange', this.checkUrl);
      } else {
        setInterval(this.checkUrl, this.interval);
      }
      return this.loadUrl();
    },

    // Add a route to be tested when the hash changes. Routes are matched in the
    // order they are added.
    route : function(route, callback) {
      this.handlers.push({route : route, callback : callback});
    },

    // Checks the current URL to see if it has changed, and if it has,
    // calls `loadUrl`, normalizing across the hidden iframe.
    checkUrl : function() {
      var current = this.getFragment();
      if (current == this.fragment && this.iframe) {
        current = this.getFragment(this.iframe.location);
      }
      if (current == this.fragment ||
          current == decodeURIComponent(this.fragment)) return false;
      if (this.iframe) {
        window.location.hash = this.iframe.location.hash = current;
      }
      this.loadUrl();
    },

    // Attempt to load the current URL fragment. If a route succeeds with a
    // match, returns `true`. If no defined routes matches the fragment,
    // returns `false`.
    loadUrl : function() {
      var fragment = this.fragment = this.getFragment();
      var matched = _.any(this.handlers, function(handler) {
        if (handler.route.test(fragment)) {
          handler.callback(fragment);
          return true;
        }
      });
      return matched;
    },

    // Save a fragment into the hash history. You are responsible for properly
    // URL-encoding the fragment in advance. This does not trigger
    // a `hashchange` event.
    saveLocation : function(fragment) {
      fragment = (fragment || '').replace(hashStrip, '');
      if (this.fragment == fragment) return;
      window.location.hash = this.fragment = fragment;
      if (this.iframe && (fragment != this.getFragment(this.iframe.location))) {
        this.iframe.document.open().close();
        this.iframe.location.hash = fragment;
      }
    }

  });

  // Backbone.View
  // -------------

  // Creating a Backbone.View creates its initial element outside of the DOM,
  // if an existing element is not provided...
  Backbone.View = function(options) {
    this._configure(options || {});
    this._ensureElement();
    this.delegateEvents();
    this.initialize(options);
  };

  // jQuery lookup, scoped to DOM elements within the current view.
  // This should be prefered to global jQuery lookups, if you're dealing with
  // a specific view.
  var jQueryDelegate = function(selector) {
    return $(selector, this.el);
  };

  // Cached regex to split keys for `delegate`.
  var eventSplitter = /^(\w+)\s*(.*)$/;

  // Set up all inheritable **Backbone.View** properties and methods.
  _.extend(Backbone.View.prototype, Backbone.Events, {

    // The default `tagName` of a View's element is `"div"`.
    tagName : 'div',

    // Attach the jQuery function as the `$` and `jQuery` properties.
    $       : jQueryDelegate,
    jQuery  : jQueryDelegate,

    // Initialize is an empty function by default. Override it with your own
    // initialization logic.
    initialize : function(){},

    // **render** is the core function that your view should override, in order
    // to populate its element (`this.el`), with the appropriate HTML. The
    // convention is for **render** to always return `this`.
    render : function() {
      return this;
    },

    // Remove this view from the DOM. Note that the view isn't present in the
    // DOM by default, so calling this method may be a no-op.
    remove : function() {
      $(this.el).remove();
      return this;
    },

    // For small amounts of DOM Elements, where a full-blown template isn't
    // needed, use **make** to manufacture elements, one at a time.
    //
    //     var el = this.make('li', {'class': 'row'}, this.model.get('title'));
    //
    make : function(tagName, attributes, content) {
      var el = document.createElement(tagName);
      if (attributes) $(el).attr(attributes);
      if (content) $(el).html(content);
      return el;
    },

    // Set callbacks, where `this.callbacks` is a hash of
    //
    // *{"event selector": "callback"}*
    //
    //     {
    //       'mousedown .title':  'edit',
    //       'click .button':     'save'
    //     }
    //
    // pairs. Callbacks will be bound to the view, with `this` set properly.
    // Uses jQuery event delegation for efficiency.
    // Omitting the selector binds the event to `this.el`.
    // This only works for delegate-able events: not `focus`, `blur`, and
    // not `change`, `submit`, and `reset` in Internet Explorer.
    delegateEvents : function(events) {
      if (!(events || (events = this.events))) return;
      $(this.el).unbind();
      for (var key in events) {
        var methodName = events[key];
        var match = key.match(eventSplitter);
        var eventName = match[1], selector = match[2];
        var method = _.bind(this[methodName], this);
        if (selector === '') {
          $(this.el).bind(eventName, method);
        } else {
          $(this.el).delegate(selector, eventName, method);
        }
      }
    },

    // Performs the initial configuration of a View with a set of options.
    // Keys with special meaning *(model, collection, id, className)*, are
    // attached directly to the view.
    _configure : function(options) {
      if (this.options) options = _.extend({}, this.options, options);
      if (options.model)      this.model      = options.model;
      if (options.collection) this.collection = options.collection;
      if (options.el)         this.el         = options.el;
      if (options.id)         this.id         = options.id;
      if (options.className)  this.className  = options.className;
      if (options.tagName)    this.tagName    = options.tagName;
      this.options = options;
    },

    // Ensure that the View has a DOM element to render into.
    _ensureElement : function() {
      if (this.el) return;
      var attrs = {};
      if (this.id) attrs.id = this.id;
      if (this.className) attrs.className = this.className;
      this.el = this.make(this.tagName, attrs);
    }

  });

  // The self-propagating extend function that Backbone classes use.
  var extend = function (protoProps, classProps) {
    var child = inherits(this, protoProps, classProps);
    child.extend = extend;
    return child;
  };

  // Set up inheritance for the model, collection, and view.
  Backbone.Model.extend = Backbone.Collection.extend =
    Backbone.Controller.extend = Backbone.View.extend = extend;

  // Map from CRUD to HTTP for our default `Backbone.sync` implementation.
  var methodMap = {
    'create': 'POST',
    'update': 'PUT',
    'delete': 'DELETE',
    'read'  : 'GET'
  };

  // Backbone.sync
  // -------------

  // Override this function to change the manner in which Backbone persists
  // models to the server. You will be passed the type of request, and the
  // model in question. By default, uses jQuery to make a RESTful Ajax request
  // to the model's `url()`. Some possible customizations could be:
  //
  // * Use `setTimeout` to batch rapid-fire updates into a single request.
  // * Send up the models as XML instead of JSON.
  // * Persist models via WebSockets instead of Ajax.
  //
  // Turn on `Backbone.emulateHTTP` in order to send `PUT` and `DELETE` requests
  // as `POST`, with a `_method` parameter containing the true HTTP method,
  // as well as all requests with the body as `application/x-www-form-urlencoded` instead of
  // `application/json` with the model in a param named `model`.
  // Useful when interfacing with server-side languages like **PHP** that make
  // it difficult to read the body of `PUT` requests.
  Backbone.sync = function(method, model, success, error) {
    var type = methodMap[method];
    var modelJSON = (method === 'create' || method === 'update') ?
                    JSON.stringify(model.toJSON()) : null;

    // Default JSON-request options.
    var params = {
      url:          getUrl(model),
      type:         type,
      contentType:  'application/json',
      data:         modelJSON,
      dataType:     'json',
      processData:  false,
      success:      success,
      error:        error
    };

    // For older servers, emulate JSON by encoding the request into an HTML-form.
    if (Backbone.emulateJSON) {
      params.contentType = 'application/x-www-form-urlencoded';
      params.processData = true;
      params.data        = modelJSON ? {model : modelJSON} : {};
    }

    // For older servers, emulate HTTP by mimicking the HTTP method with `_method`
    // And an `X-HTTP-Method-Override` header.
    if (Backbone.emulateHTTP) {
      if (type === 'PUT' || type === 'DELETE') {
        if (Backbone.emulateJSON) params.data._method = type;
        params.type = 'POST';
        params.beforeSend = function(xhr) {
          xhr.setRequestHeader("X-HTTP-Method-Override", type);
        };
      }
    }

    // Make the request.
    $.ajax(params);
  };

  // Helpers
  // -------

  // Shared empty constructor function to aid in prototype-chain creation.
  var ctor = function(){};

  // Helper function to correctly set up the prototype chain, for subclasses.
  // Similar to `goog.inherits`, but uses a hash of prototype properties and
  // class properties to be extended.
  var inherits = function(parent, protoProps, staticProps) {
    var child;

    // The constructor function for the new subclass is either defined by you
    // (the "constructor" property in your `extend` definition), or defaulted
    // by us to simply call `super()`.
    if (protoProps && protoProps.hasOwnProperty('constructor')) {
      child = protoProps.constructor;
    } else {
      child = function(){ return parent.apply(this, arguments); };
    }

    // Set the prototype chain to inherit from `parent`, without calling
    // `parent`'s constructor function.
    ctor.prototype = parent.prototype;
    child.prototype = new ctor();

    // Add prototype properties (instance properties) to the subclass,
    // if supplied.
    if (protoProps) _.extend(child.prototype, protoProps);

    // Add static properties to the constructor function, if supplied.
    if (staticProps) _.extend(child, staticProps);

    // Correctly set child's `prototype.constructor`, for `instanceof`.
    child.prototype.constructor = child;

    // Set a convenience property in case the parent's prototype is needed later.
    child.__super__ = parent.prototype;

    return child;
  };

  // Helper function to get a URL from a Model or Collection as a property
  // or as a function.
  var getUrl = function(object) {
    if (!(object && object.url)) throw new Error("A 'url' property or function must be specified");
    return _.isFunction(object.url) ? object.url() : object.url;
  };

})();